Method and apparatus for helically welding strip material



J. W. BROWN, JR. ET

METHOD AND APPARATUS FOR HELICALLY WELDING STRIP MATERIAL April 9, 196810 Sheets-Sheet 1 Original Filed June 6, 1963 INVENTORS. 6P0 WM 12. z.

.70/7A/ W. ROBERT 14/ AAASE BY BoowMI/L Z/fmawiu.

A 77-0RNEK5' April 9, 1968 -J BROWN, JR" ETAL 3,377,459

7 METHOD AND APPARATUS FOR HELICALLY WELDING STRIP MATERIAL I OriginalFiled June 6, 1963 l0 Sheets-Sheet 2 INVENTORS. JUH/V w aeowlv we a05527 W. A/AASE Bowen/via, 34M Wig M )477 0/( /Vf April 1958 I .1.BROWN, JR, ET AL 3,377,459

I METHOD AND APPARATUS FOR HBLICALLY WELDING STRIP MATERIAL OriginalFiled June 6,1965

10 Sheets-Sheet 3 INVENTORS. JOHN W BAOW/VJZ. A

05527 I44 KAASE April 9, 1968 J. w. BROWN, JR, ET 3,377,459

METHOD AND APPARATUS FOR HELICALLY WELDING STRIP MATERIAL Original FiledJune a, 1963 10 Sheets-Sheet 4 INVENTORS. vm I v JOHA/ WBFOWA/JR 41'05587 w. KAASL BMWM S April 9, 1968 Y J. W. BROWN, JR. ET AL 3,377,459

WELDING STRIP MATERIAL METHOD AND APPARATUS FOR HELICALLY l0Sheets-Sheet Original Filed June 6, 1963 4 W m w 2 M m B MA W WM W 0% mJ MB April 9, 1968 J. w. BROWN, JR. ET AL METHOD AND APPARATUS FORHELICALLY WELDING STRIP MATERIAL Original Filed June a, 1963 10Sheets-Sheet 6 INVENTOKS. JOHN yv. ak'ow/v me. a? B05587" W 'KAASE Ban,8

J. w. BROWN, JR. ET AL 3,377,459

WELDING STRIP MATERIAL A ril 9, 1968 METHOD AND APPARATUS FOR HELICALLYl0 Sheets-Sheet '7 Original Filed June 6, 1963 April 17968 .1. w. BROWN,JR, ET AL 3,377,459

METHOD AND APPARATUS FOR HELICALLY WELDING STRIP MATERIAL 1OSheets-Sheet 5 Original Filed June 6,1963

JOHN I/V, aeow/v JP. 4

INVENTORS.

FJQ

ROBERT W KAAS'E April 9, 1968 j w, BROWN, JR" ET AL 3,377,459

METHOD AND APPARATUS FOR HELICALLY WELDING STRIP MATERIAL 1OSheets-Sheet 9 Origin a1 Filed June 6, 1963 INVENTORS. JOHN W. E/POW/VJR;

1905527 PM KAASE:

KI ,4 fraFA/f j April 9, 1968 J. w BROWN, JR ET AL 3,377,459

WELDING STRIP MATERIAL METHOD AND APPARATUS FOR HELICALLY OriginalF'iled June 6, 1963 10 Sheets-Sheet 10 1 i z v 5?. E 2% M N 0 w m ww 5 Wv if BYB United States Patent Claims. (Cl. 219-107) ABSTRACT OF THEDISCLOSURE Apparatus and method for bending and welding a metal striphelically on edge about a generally cylindrical member utilizing highfrequency electrical current, according to which an electrode is appliedto the generally cylindrical member and another electrode is applied tothe side of the metal strip that faces the edge thereof that is weldedto the generally cylindrical member.

Cross-reference to related application This application is acontinuation of applicants copending application Ser. No. 285,953, filedJune 6, 1963.

Description This invention relates to method and apparatus for helicallywelding metal strip material on the outer surface of an elongated metalmember of generally circular cross section, and to helically finnedtubes that may be produced thereby.

While capable of other applications, the invention provides particularadvantages in the manufacture of transversely finned tubes for use inheat exchangers in which one heat exchange fiuid passes through such atube and another heat exchange fluid passes outside of the tubetransversely thereof. In order to achieve the desired large heattransfer area, the outer surface of the tube has closely spaced finsthat extend radially transversely of the tube. It is advantageous tomake such a finned tube by welding a strip of metal along one of itsedges in a helical path onto the outside of the tube to form the fins;the weld preferably should be homogeneous and continuous to provide goodheat conductivity between the tube and the fin.

An object of the present invention is the provision of method andapparatus for rapidly and economically manufacturing high qualityelongated members having strip material welded thereon in a helicalpath, at a high rate of production with little or no loss due tosubstandard manufacturing. A further object is the provision ofadjustable apparatus which can be used to weld fins or the like ofvarious depth on tubes or other generally circular elongated members ofa wide variety of sizes, in helices of various pitches. Another objectis the provision of a finned tube, suitable for heat exchange purposes,comprising a helical fin of thin metal that is welded throughout itslength to the exterior of the tube, the lower portion of the finimmediately adjacent the tube being substantially thicker than theremainder of the fin to provide a relatively wide juncture with the tubeand good heating conductivity.

These and other objects of the invention will be apparent from thefollowing description in connection with the accompanying drawings inwhich:

FIGURE 1 is a front elevation of one form of apparatus embodying theinvention, shown as used for welding a strip of metal on a tube to forma helically finned tube, parts of the cooling liquid sump being brokenaway for clearness;

FIGURE 2 is a plan of the apparatus of FIGURE 1, to the same scale;

FIGURE 3 is an elevation, from line 3-3 of FIGURE 2, of the weldingportion of the apparatus, to an enlarged scale;

FIGURE 4 is a plan of the FIGURE 3, from line 4-4 same scale;

FIGURE 5 is an elevation of the tube-advancing unit of the apparatusfrom line 5-5 of FIGURES 1 and 6, to a scale larger than that of any ofthe preceding figures;

FIGURE 6 is a side elevation of the unit of FIGURE 5 from line 6-6thereof and to the same scale, parts being broken away to show means foradjusting the angle of skew of the axis of one of the drive rollersrelatively to the axis of the tube;

FIGURE 7 is a diagrammatic plan showing a tube to which the helical finis being welded according to the invention, this plan also indicatingthe general relationship of the skewed rollers that support, rotate andadvance the tube longitudinally thereof, and a roller that guides andholds down the strip being welded on the tube;

FIGURE 8 is a detail view, along line 8-8 of FIG URE 3 and to a largerscale, of the tube and the portion of the apparatus embodying theelectrodes that contact the strip being welded to the tube, the tubebeing shown in broken lines; 1

FIGURE 9 is a side elevation of the tube-contacting electrode means,generally along line 99 of FIGURE 8 and to a somewhat smaller scale;

FIGURE 10 is a sectional view along line 10-10 of FIGURE 9 and to thesame scale;

FIGURE 11 is a side elevation of the fin-contacting electrode means fromline 11-11 of FIGURES 8 and 12, to the same scale as FIGURES 9 and 10;

FIGURE 12 is a sectional view from line 12-12 of FIGURE 11 and to thesame scale;

FIGURE 13 is a detail elevation, along line 13-13 of FIGURE 8 and to thesame scale as FIGURES 912, showing details of the support for thefin-contacting electrode, and also showing the relationship of thetube-contacting and fin-contacting electrodes;

FIGURE 14 is a fragmentary side elevation to a scale larger than that ofany of the preceding figures, of a portion of a helically finned tubeembodying the invention; and

FIGURE 15 is a section along line 15-15 of FIG- URE 14 but to a largerscale, of one of the fins welded to the tube, particularly showing thebroader base portion of the fin that is welded to the tube.

General arrangement.-As indicated in the drawings, and particularly inFIGURES l, 2, 3 and 7, the illustrated apparatus supports, rotates andlongitudinally advances a tube T with its axis essentially coincidentwith a pass line A so the tube moves in the direction indicated by thearrows, while welding a thin strip of metal S to the exterior of thetube T in a desired helical path to form spaced helical fins F.

. The apparatus comprises a fixed base 1 rigidly carrying an adjustabletube rotating and advancing unit 2. that is driven through transmissionunit 3 and air operated clutch 4 from a conventional variable speedpower unit 5; clutch 4 is engaged and disengaged as required, while theunit 5 operates continuously. Base 1 also carries an adjustable weldinghead 6 that guides the strip S to the tube T at an angle suitable forforming a helix having the desired spacing between the turns, aids thetube in bending the strip edgewise around the surface of the tube, andwelds the bottom edge of the strip to the tube in a desired helical pathby suitable electrical current of at least about 50,000 cycles persecond frequency. The weldportion of the apparatus of of FIGURE 3 and tothe ing head 6 is mounted on base 1 so it can be adjusted and rigidlyheld in various positions about an axis B that is essentiallyperpendicular and vertical to, and essentially intersects, the pass lineA. The welding current is supplied from a suitable commerciallyavailable source 7 through a commercially available transformer 8. Thestrip S is drawn from a coil C on a rotatable drum 9; the edge to bewelded of the strip preferably is square and smooth. The finned portionof the tube leaving the welding head moves over a support 10 whichsupports the tube while permitting it to rotate and move longitudinally.Base 1 is surrounded by a sump It: for collecting cooling liquid that isrecirculated conventionally.

Tube rotating and advancing unit.The tube drive unit 2 (FIGURES 5, 6 and7) for rotating and advancing the tube T comprises a frame 11 fixed tobase 1 through adjusting block 12. Frame 11 supports three rollers 13,14 and 15 essentially equiangularly spaced around the pass line A inskewed tube-gripping and advancing relation.

Each roller comprises two spaced roller portions 16 and 17 rigidlydemountably fixed to an axle 18 by suitable conventional means notshown. Each roller portion preferably has a tube-engaging surface 19that is tapered to decrease in size toward the other roller portion, toaid in gripping the tube; the surfaces 19 may be knurled to increasefriction. Each roller 13, 14 and 15 can be adjusted so it axis ofrotation R is in a desired fixed skewed relation to the pass line A.

To accomplish this, the axle 1 8 of each lower roller 13 and 14 isjournaled in a supporting member 21 (see FIGURE 5), that includes a stem22 of circular cross section about an axis U perpendicular to andintersecting the pass line A and the center of the axis of rotation R ofthe roller carried by the member 21. The stem 22 is mounted forrotatable adjustment about'axis U in a block 23 rigidly fixed to thespaced side plates 24 of frame 11; the side plates having openings 25through which the tube T travels. Stem 22 is nonrotatably fixed to amember 27 (FIGURES 5 and 6) having an arm 28 carrying an indicatingpointer 29; the stem also has a threaded end carrying lock nuts 31.Block 23 rigidly supports a bracket threadedly carrying adjusting screws33 bearing against one of the sides of member 21; block 23 also carriesan indicating dial 34 having markings 35 adjacent pointer 29 to indicatethe amount of skew of the axis R of the associated roller.Roller-supporting member 21 can thus be adjusted and locked in a desiredangular position by the adjusting screws 33 and lock nuts 31, with theaid of arm 28, pointer 29 and dial 34.

The uppermost roller 15 (FIGURES 5 and 6) can be similarly adjusted andlocked so its axis R is in any one ofv a variety of skewed positions asdesired, but it also may be adjusted so its axis R may be moved towardor away from the pass line A to cause the tube T to be firmly engaged byall three skewed rollers. As shown in FIGURES 5 and 6, the axle 18 ofroller 15 is journaled in a supporting member 36 having a stem 37circular in cross section about an axis U that is perpendicular to andintersects both pass line A and the center of axis R of roller 15. Stem37 is rotatably adjustably mounted in a vertically adjustable member 38rigidly carrying a transverse member 39 at its upper end. This member 38is slidably but not rotatably mounted in frame 12 of unit 2, by guideportions 41 that engage cooperating guide portions in a block 42 rigidlyfixed between side plates 24 of frame 11. The upper portion of stem 37of supporting member 36 has keyed to it an adjusting member 27 carryingan arm 28 and a pointer 29 movable angularly when member 36 is adjustedabout its axis to indicate the angular adjustment by markings on a dialportion of member 39.

The assembly comprising the adjustable member 38, theroller-supportingmember 36, and the roller 15 can be adjusted toward and away from thepass line A and locked in the adjusted position by set screws 43, havinglock nuts 44, threaded into transverse member 39 and operating incompression with their lower ends bearing against the top of frame 11,and by cap bolts 45, having nuts 46, extending in tension between thecross member 39 and frame 11 as shown in FIGURE 5.

The angle of skew of the axis R of roller 15 can be adjusted relativelyto pass line A, and the roller can be locked in place at the desiredangle, by bolts 47 threaded in bracket 48 on the frame 11 and bearingagainst supporting member 36, and by lock nuts 49 on the end of stem 37.

The axes U about which the supporting members 21 for rollers 13 and 14and the supporting member 36 for roller 15 are pivotally adjustableintersect the axes R of their respective rollers and the pass line A,and are preferably equiangularly spaced about the pass line .A in aplane normal to the pass line; in normal operation the parts areadjusted as indicated so that the axes R are essentially equally spacedfrom and equally skewed in the same direction to the pass line A.

The rollers 13, 14 and 15 of unit 2 are positively driven in anyposition to which they may be adjusted about the axes R since, as shownin FIGURES 1, 2 and 6, each of their shafts 18 is connected to universaljoint 51, intermediate shaft 52, and universal joint 53 to one of theshafts 54 of the transmission unit 3 connected to the drive system 4.

Transmission unit.The transmission unit 3 (FIG- URES 2 and 3) includes aframe 55 fixed to base 1 through an adjusted block 56. The frameincludes upwardly extending plate frame members 57 apertured for passageof tube T. The three shafts 54 are journaled in these members 57 aboutaxes equidistantly and equiangularly spaced around the pass line A.Shafts 54 are simultaneously rotated in the same direction and at thesame speed by a chain belt 58 passing around sprockets 59 fixed to theshafts. One shaft 59 is driven by gear "61 rotated by gear 62 mounted ona countershaft 63 driven by drive means 4 from power unit 5.

The tube T is thus simultaneously rotated and advanced from the weldinghead 6 at a predetermined speed of rotation and advance. For a tube ofgiven size, the speed of rotation can be adjusted by adjustment of thespeed of the power unit 5, and the amount the tube advances during eachrevolution can be predetermined by adjusting the skew angles of therollers 13, 14 and 15 of the unit 2 as described above. Within limits,tubes of larger or smaller sizes than those predetermined by thedimensions of the unit 2 may be handled by changing the sizes of therollers 13, 14 and 15; if it is desired to handle tubes of larger orsmaller sizes than can be accommodated by changing rollers in a givenunit 2, the unit itself may be replaced by another in which the axes ofthe rollers are radially spaced at a suitable distance from the passline A. To facilitate this, adjusting block 12 on which unit 2 ismounted may be replaced by another block of suitable thickness. Theadjusting block 56 on which the transmission unit 3 is mounted may alsobe changed if necessary. ,7

Welding head.The welding head 6 (FIGURES 1 to 4 and 8 to 13) comprises abase member 64 that is mounted on base 1 for pivotal adjustment about anaxis B (FIGURES l, 2 and 3) that is essentially vertical and intersectsthe pass line A. As shown in FIGURE 4, base member 64 is a plategenerally T-shaped in plan having a parallel-sided front portion 65 anda wider rear portion 66. Front portion 65 has a hole through which astud 67 extends into the top of the top of the base member 64 for thedesired pivotal movement about axis B. The member 64 has curved slots68, centered on axis B, through which project locking bolts 69 threadedinto base 1. Base member 64 thus can be adjusted to and locked in anyone of a variety of angular positions about axis B.

A pedestal 71 is rigidly mounted at one side of the rear portion 66 ofbase member 64 to clear the strip S as it passes to the tube T. Pedestal71 is made up of lower part 71a, upper part 7112, and a replaceableplate 71c (FIG- URE 3) to permit vertical adjustment of the partscarried by the pedestal. Pedestal 71 carries high frequency transformer8, which as shown in FIGURES 1 and 2, at its lower side edges has lugs72 that are clamped by gibs 73 and bolts 74 to permit the transformer tobe slidably adjusted toward and away from the axis A in a path parallelto the sides of the base member 64, and be clamped in the desiredlocation. This permits the welding electrodes 75 and 76 (FIGURES 3,9-13) that respec-' tively contact the tube and fin and that aresupported from the transformer 8, to be adjusted toward or away from thepass line A.

The front portion 65 of base member 64 also rigidly adjustably carries afin hold-down unit 77 (FIGURES 1-4) that is adjustable longitudinallyand transversely of portion 65. To achieve this, a base plate 78 ismounted on portion 65 by key means 79 (FIGURE 1) and bolts 81 threadedinto base member 64 and extending through slots 82 in member 78 (FIGURE4) so that member 78 can be adjusted longitudinally of portion 65 andclamped in place. Another base plate 83 is adjustably mounted on member78 by bolts 84 threaded into member 78 and extending through slots 85 inmember 83 (FIGURE 4) and by screws 86 that bear against the sides ofmember 83 and are threaded in brackets 87 fixed to the side edges offront portion 65 of base member 64, so that member 83 can be adjustedtransversely of member 64 and locked in place.

The fin hold-down unit 77, as shown in FIGURES 14, comprises an uprightsupport 88 rigidly mounted on base member 83 and at its upper endpivotally carrying on shaft 89 an arm 91. One end of the arm isconnected to a piston rod 92 of an air cylinder 93 the lower end ofwhich is pivotally connected at 94 to the support 88. The other end ofarm 91 rotatably carries a grooved roller 95 (FIGURES 1-4 and 7), thegroove 96 of which engages the strip S where it begins bending edgewisearound the tube to guide the strip and hold it down in the tube as itbends. This roller preferably is formed of heat resistant metal thatwill not weld to the metal of the fin or the tube, such as a suitablecopper alloy like that sold under the name Ampoo. The radial groove 96is wide enough to receive the strip but narrow enough accurately toguide it, and deep enough to facilitate the guiding and holding down ofthe strip but less deep than the width of the strip. A set screw 97,threaded into a bracket 98 fixed to frame 88, engages arm 91 to limitadjustably the movement of the roller 95 toward the tube T.

The groove of the roller thus can be adjusted to be in any desiredposition angularly and transversely relatively to the pass line A, andthe roller can be positively moved toward and away from the tube T bythe air cylinder 93.

Base 1 also carries a supporting roller 101 (FIGURES 1, 3 and 4) locatedbeneath the tube T engaging the outer edges of several of the fins F toprevent undesired downward deflection of the tube under the forcesresulting from edgewise bending of the strip S and from the upper roller95. Roller 101 is journaled in a bracket 102 that is rigidly fixed butpivotally adjustable about a vertical axis on a frame 103 rigidly butvertically adjustably mounted on a support 104 fixed to base 1. By suchadjustable supporting means, the roller may be adjusted vertically tocontact the fins at the lower portion of the tube, being wide enough tocontact several fins, and can be angularly adjusted about a verticalaxis so the axis of rotation of the roller is perpendicular to thedirection of the fins at the points of contact of the roller with thefins, to provide rolling supporting contact.

Electrode supporting means-The means for holding the welding electrodes75 and 76 in slidable contact with the strip and the tube to supply thewelding current that forms the welded joint between the strip and thetube are shown in FIGURES 3 and 8 to 13 inclusive. These electrodes aresupported from two spaced electrically isolated power supply bars 105and 106 extending downwardly from and forming part of transformer 8.These bars preferably are formed of copper or other metal having thedesired strength and electrical conductivity, are provided with watercooling openings 107 and 108, and have flanged bottom portions to whichare bolted the electrode supporting means described below.

As shown in FIGURES 8-10, the means for supporting the tube-contactingelectrode 75 comprises a downwardly extending bracket 111 fixed byscrews 112 to the bottom of the electrode bar 105. The lower end of thisbracket slidably supports for movement toward and away from the passline A a member 113 on which the electrode 75 is mounted. Slide member113 is thus supported by a guide member 114 bolted to the bottom ofbracket 111 and by gibs 115 bolted to guide member 114. At its endnearest the pass line A member 113 carries a member 116 having adove-tail portion 117 extending parallel to pass line A; this portion isclamped onto the end of member 113 by gib 118. Member 116, to which theelectrode 75 is fixed, thus can be adjusted axially of the tube toprovide a desired relation with the fin and fin-contacting electrode 76,and then rigidly clamped in place; the member 116 and electrode 75 canreadily be removed for repair or replacement of the electrode.

Slide member 113 may be positively moved toward and away from tube T toengage and disengage the electrode 75 and to permit the welding of tubesof different diameters, by an air cylinder 119 mounted on a bracket 121bolted to the bracket 107 and extending away from the pass line, the aircylinder piston rod 122 being connected to the slide member 113.

Preferably bracket 111 has bores 123 (FIGURES 9 and 10) communicatingwith openings 107 and 108 of transformer electrode bar 105 to permitcirculation of cooling fluid; the member 116 may have bores 124 topermit circulation of cooling fluid by tube 125.

The means for supporting the electrode 76 contacting the strip S beingwelded is shown in FIGURES 8, ll, 12 and 13. It comprises a downwardlyextending bracket 126, formed of copper or other suitable electricallyconductive metal, fixed to the bottom of bracket 106 by bolts 127. Aslide member 128, to which is fixed the fin-contacting electrode '76, isslidably mounted on bracket 126 by guides 129 and 130, shown in FIGURE13, for movement parallel to pass line A, so that electrode 76 can beengaged with and disengaged from the strip S as desired.

To positively move slide member 128 there is an air cylinder 132 thepiston rod 133 of which is connected to member 134 fixed to slide member128 (FIGURE 8). Cylinder 132 is mounted on a bracket 135 fixed to aplate member 136 formed of electrical insulating material such assuitable hardboard of sufficient strength and thickness for thepurposes. Member 134 slides in a sleeve 137 fixed in member 136. Member136 itself is rigidly supported by two cross members 138 (FIGURES 8 and9) that are rigidly carried by a plate member 139, which may be ofmetal, fixed by bolts 141 to the bracket 111 supporting the tubeelectrode (FIGURE 8).

Member 136 also carries another plate member 142 of substantially thesame outer configuration as plate member 136 below the cross members138. Plate members 136 and 142 are recessed to define at their juncturea groove 143 extending from the rear of said plate members to the frontthereof to conduct the strip S into close proximity to the tube T in apath parallel to the sides of the front portion 65 of the base platemember 64, so that said path brings the strip S to the tube at theproper angle relative to the pass line A and the tube to form thedesired helical turns as the tube rotates. The recess in plate member136 contains a metal strip 144 (FIGURE 8) that acts as a wear andadaptor strip that can be replaced by other strips of differentthickness and grooved configurations to modify recess 143 so it canreceive and guide strips S of various thicknesses and widths.

As shown in FIGURE 3 another guide member 145 is bolted to the upperportion of pedestal 71 to guide the strip S from the rear of thepedestal close to the rear edges of plates 136 and 142; this guidemember, which may be formed of suitable wear resistant material, may beadjusted or changed to accommodate strips of different sizes.

The bracket 126 preferably has bores 146 (FIGURES 12 and 13)communicating with openings 107 and 108 of transformer electrode bar 106to permit circulation of cooling fluid. Slide member 128 is alsosuitably bored for cooling fluid, which may be circulated throughcooling tubes 147 (FIGURES 8, 11-13). If desired, cooling water or thelike maybe sprinkled on the roller 95 and the tube T and strip S in thevicinity of weld point W by suitable conventional means not shown.

A sheet 148 of electrical insulating material (FIGURE 8) preferably islocated between transformer bars 105 and 106 and brackets 111 and 126 toprevent arc-over.

perati0n.A preferred method of welding a fin of a desired depth andthickness in ahelix of a desired pitch on a tube of a desired outerdiameter includes the following operations: A tube-rotating andadvancing unit 2 having a frame 11 and a supporting adjusting block 12to permit the unit 2 to handle a range of tube sizes including the sizeof tube to be welded is first selected and mounted on the base 1 if theunit 2 and adjusting block 12 already in place are not suitable. Ifnecessary, the rollers 13, 14 and 15 of the unit 2 are replaced by theother rollers which will handle a tube of the size desired. The skewangle of each roller is then adjusted as described above so that as therollers rotate they advance the tube T the desired amount during eachrevolution to produce a desired helical pitch of the fin. If necessarythe transmission unit 3 which drives the unit 2 is adjusted as indicatedpreviously.

If necessary plate 710 of the pedestal 71 is replaced by another plateof suitable thickness in order to cause the strip S traveling throughthe guide means 145 and the slot 143 of the electrode supporting meansmounted on transformer member 106 to contact the periphery of the tube Tat the proper distance above the pass line A; the adaptor strip 114 insuch electrode supporting means is changed if necessary to accommodatethe strip.

Before or at this time the angle of inclination of the Welding headportion of the apparatus relative to the pass line A is adjusted aboutthe axis B and, if necessary, the base members 78 and 83 are adjustedlongitudinally and transversely of the base member 74 so that the groove96 of the upper roller 95 can engage the fin at the proper helix anglerelatively to the axis of tube T to produce a helix of the desiredpitch. This is facilitated since the roller 95 is so carried by thewelding head portion that the axis of the roller is at all timesperpendicular to that portion of the strip S first contacting tube T.

The roller 95 is then retracted upwardly to clear the tube.

The free end of the strip S is then manually threaded through the guide145 on the pedestal 71 and the slot 143 on the electrode-supportingmeans carried by the transformer bar members 105 and 106, and is pulledforwardly over and past tube T. This free end is then curved in theplane of the strip for a short distance so its lower edge can fit theouter surface of the tube. The strip is then moved back until thiscurved free end contacts the top of the tube. This curved end is thenfixed to the tube, as by spot welding in a known manner. The pressingroller '95 is then moved downwardly into operating position by aircylinder 93, the hitherto retracted electrode 75 is brought into contactwith the tube by air cylinder 119, and the hitherto retracted electrode76 is caused to contact the strip S by air cylinder 132. At this time,or after the few helical fin turns have been welded, the lower or back--up roller 101 is adjusted by raising it so the upper por- 8 tion ofitsperiphery contacts the lower portion of the fins welded on the tubeand by adjusting its angle of inclination to the pass line A to providepure rolling contact with the fins as described above.

The electrical portion of the apparatus is adjusted to supply highfrequency current of suitable characteristics having a frequency on theorder of 50,000 cycles per second or preferably considerably higher, forexample, 350,000 to 450,000. cycles per second. The cooling fluid iscaused to circulate through the various bores and passages provided forthat purpose. The tube is then rotated by the tube rotating andadvancing unit 2 driven by the transmission unit 3 for one or a very fewturns, with the welding current off to test the adjustment of the partsand to test whether the free end of the strip is secured to the tube.The welding current is then turned on.

During welding, the electrode slidingly contacts the tube close to thelocation W at which the strip S first contacts the tube (FIGURES 3, 8,11 and 13) but at a sufficient distance from the strip to preventarc-over between the electrode and the strip; electrode 75 is preferablysubstantially aligned transversely to the tube T with the electrode 76and location W, as shown in FIGURE 8.

The electrode 76 slidingly contacts one side of the strip S at its lowerportion, preferably so the bottom of the electrode is essentiallyadjacent the bottom edge of the strip as shown in FIGURES 11 and 13, thedistance from the electrode to the location W at which the strip firstcontacts the tube T, however, being substantially greater than thedistance of electrode 75 from location W (see FIGURE 13). Since theelectrode 76 slidingly contacts the side of the strip, there can be asubstantial area of contact which permits efiicient passage of electriccurrent between the electrode and the strip and which prevents localizedundesired overheating where the electrode 76 contacts the strip.

Consequently, welding cur-rent will flow on the tube along a short pathextending between electrode 75 and location W, and along the lowerportion of the strip S between location W and electrode 76 as indicatedby the broken lines 150 in FIGURE 13. This current causes the lowerportion of the strip S and the surface of the tube at the location W,which is of relatively small area, to be heated to welding temperature.Only the surface portions which come into contact at the weldinglocation W ordinarily will be heated to the welding temperature and thenonly to a very shallow depth of metal, on the .order of a fewthou-sandths of an inch, the portions of the strip S and the tube awayfrom the welding location W being substantially cooler because of theskin heating effect of the current and because .of heat radiation fromthe tube and fin surfaces. Therefore, such more remote portions of thetube and tin are strong and hard enough to permit the surfaces of thestrip S and the tube at the location W to be brought together by theroller under sufficient force to produce a homogeneous continuous weldas the tube rotates and the strip S is fed to the tube.

Since only the portion of the strip in the vicinity of the weldinglocation W is appreciably softened by heat and the cooler more remoteportions of the strip are of substantially un'dirninished hardness andstrength, several advantages are provided.

The inner edge portion of the strip being formed into a fin defines ashorter length around the tube than does the outer edge portion; a largeportion of the upset-type deformation of the fin metal due to thisdifference in length can be localized in the softened portion of thetfin adjacent the tube, although the portion of the strip nearer itsouter edge appears to be stretched somewhat also to compensate for suchdifferences in lengths between the inner and outer edges of the strip.The metal in the portion of the fin immediately adjacent the tube iscompressed longitudinally of the fin due to the length difference, andtransversely of the fin by the roller 95, so

that the softened metal in the portion .of the fin immediately adjacentthe tube can broaden to thickness considerably greater than in theremainder of the fin as the welded joint is formed, as shown in FIGURE15. This broadening also tends to be thus localized to the portion ofthe fin between the roller and the tube, by the groove 96 of roller 95.

FIGURE 15 shows a preferred finned tube structure in which the lowerportion '151 of the fin F immediately adjacent to the tube T isconsiderably wider than the remainder of the fin, substantiallyuniformly throughout the length of the fin. This widened portion of thefin provides a greater welding area and hence a stronger weld joint,more stability of the fin and greater resistance to tilting relativelyto the tube, a stronger fin, and more cross sectional area at thejuncture of the fin and tube for effective transmission of heat betweenthe tube and the fin. The heating and broadening of the portion of thefin adjacent to the tube also inhibits tendencies of the fin metal toWrinkfle during the bending and welding of the fin.

As the tail end of a tube section T being welded approaches the vicinityof the drive unit 2 the welding current is cut off and the tube driveunit 2 halted. The roller 95 is raised and the strip S is cut from thefinned tube. A succeeding tube section is passed through transmissionunit 3 until its leading end abuts the tail end of the tube sectionhaving fins thereon. The drive unit 2 is started and the tail andleading end portions of the tubes are passed through unit 2 until theleading end of the unfinned tube passes under the roller 95. The abovedescribed process of starting the finning operation on the new tube isthen repeated.

When the tail end of strip S reaches the immediate vicinity of thewelding point W, the welding current is cut off and the operation of theapparatus is halted. The upper roller 95 is retracted and the leadingend of the succeeding strip S from a new coil is threaded through theapparatus and brought into the vicinity of the welding point, where itmay be spot welded to the tail end of the preceding strip S, or curvedand welded to the tube as described above. Roller 95 is lowered intowelding position, and the apparatus is started. Thus very little time islost in starting a new strip.

The invention may be employed for applying helical fins or strips totubes or pipes or other curved surfaces of steel, copper, aluminum orother metals or alloys thereof by suitable adjustment of the weldingcurrents and the welding pressures. Although the invention has beendiscussed in connection with the application of welded hellical fins totubes, it may be employed to apply other types of helical strips toother elongated members of generally circular cross section, such asbars or rods.

The above and other modifications of the invention will be apparent tothose skilled in the art. It is intended the patent shall cover bysuitable expression in the appended claims whatever features ofpatentable novelty reside in the invention.

We claim:

1. Apparatus for bending and welding a metal strip having a single crosssection helically on one of its edges about a generally cylindricalmember having an axis, comprising means for supporting such generallycylindrical member, means for guiding the strip on edge at a desiredhelix angle relative to the axis of said generally cylindrical memberand in a position whereby an edge of said strip advances generallytangentially into pressure engagement with said member at a weldinglocation, means for effecting relative rotation between said generallycylindrical member and said strip and for effecting axial movement ofsaid strip relative to said welding location, a source of electricalcurrent of a frequency of at least about 50,000 cycles per second, anelectrode connected to one terminal of said source and mounted to engagesaid cylindrical member at a point on the circumference thereof inadvance of the welding location, another electrode connected to theother terminal of said source and mounted in a position to engage saidstrip substantially in advance of said welding location at a side ofsaid strip at only a portion of said strip closely adjacent the edgethat engages such generally cylindrical member, said source beingadapted to supply sutficient current at said frequency to said memberand said strip to heat only said edge portion of said strip and saidgenerally cylindrical member at said welding location sufficiently tocause said edge of said strip and said surface to be welded withoutheating the remainder of the width of said strip sufficiently todiminish substantially the strength and hardness of the metal thereinand without use of heating means other than said electrodes and thecurrent supplied to said electrodes.

2. The apparatus of claim 1 in which the distance from the electrodecontacting said strip to said welding location is substantially greaterthan the distance from said electrode contacting said member to saidwelding location.

3. The apparatus of claim 1 comprising means for supporting saidgenerally cylindrical member for rotation about its axis and means forguiding said strip to said generally cylindrical member in a fixed path.

4. The apparatus of claim 3 in which said means for supporting saidgenerally cylindrical member comprises a plurality of rollers forengaging said member at spaced points about the circumference thereof,at least one of said rollers being driven, said rollers being mountedabout axes extending in spaced skewed relation to the axis of saidmember to cause said rollers to advance said member longitudinally pastsaid welding location while rotating said member about its axis andsupporting said member.

5. The apparatus of claim 4 in which said rollers are adjustable tochange the skewed relation thereof to change the distance said generallycylindrical member travels during each revolution thereof.

6. In a welding apparatus for welding a helical strip of metal on anelongated generally cylindrical member, means for rotating and advancingthe elongated member axially thereof along a pass line comprising aplurality of rotatable rollers adapted to engage the outer surface ofsaid generally cylindrical member, said rollers being individuallyrotatable about axes extending generally longitudinally of said passline and spaced around said pass line, and means for adjustablyrotatably supporting said rollers so that the axis of rotation of eachroller may be adjusted to a skewed relation to the pass line about anaxis normal to said axis of rotation and normal to said pass line, oneof said rollers being adjustably mounted for movement toward and awayfrom said pass line.

7. In a welding apparatus for welding a helical strip of metal on anelongated generally cylindrical member, means for rotating and advancingthe elongated member axially thereof along a pass line comprising aplurality of rotatable rollers adapted to engage the outer surface ofsaid generally cylindrical member, said rollers being individuallyrotatable about axes extending generally longitudinally of said passline and spaced around said pass line, and means for adjustablyrotatably supporting said rollers so that the axis of rotation of eachroller may be adjusted to a skewed relation to the pass line about anaxis normal to said axis of rotation and normal to said pass line, eachof said rollers comprising two generally frusto-conical portions spacedalong the axis of rotation of said roller on opposite sides of theintersection of said axis with the axis normal thereto about which saidaxis of rotation is adjusted, the smaller portion of each of saidfrusto-conical portions being closer to said point of intersection thanthe larger portion thereof.

8'. The method of applying, bending, and Welding an advancing metalstrip having a single cross section on an edge thereof to a metalsurface that advances relatively to the strip while veering away fromthe strip in the direction of advance, which method comprises applyingthe terminals of a source of high frequency current respectively to thestrip and to said surface at points thereon in advance of the point ofapplication of the strip'to said surface, for heating said surface andsaid edge of the strip contacting said surface to welding temperature ata welding location where said edge and said surface come into contact,said current being applied to said strip substantially in advance ofsaid welding location at a side of said strip at only a portion of saidstrip closely adjacent the edge of said strip which is to be Welded tocause current to flow along the surface of the portion of said stripclosely adjacent said edge to be welded to said welding location andthence from said welding location along said surface of the metal memberto the other terminal of the current source, pressing said strip againstsaid metal member with substantial force directed transversely of thestrip in the vicinity of said welding location, said current being of afrequency of at least about 50,000 cycles per second and sufficient toheat the portion of the metal member and only said edge portion of saidstrip that is to be welded in the vicinity of said welding location tothe welding temperature and to a degree such that said strip edgebecomes continuously welded to the member, without any substantialheating other than that caused by said flow of current so applied tosaid strip and said surface.

9. The method of claim 8 comprising pressing said strip against saidsurface with sufficient force directed 12 transversely of the strip inthe vicinity of said welding location, and with sufficient heating ofthe strip due to said application of current, to cause only the portionof said strip closely adjacent said metal surface to widen substantiallydue to compression of the metal along said edge portion while said stripbends along said surface.

10. The method of claim 9 in which said strip is pressed against saidmetal surface by the radial groove of a radially grooved roller rotatingabout an axis perpendicular to the strip at the location at which it iswelded, said groove being of a depth sufficient to extend substantiallyacross the portion of the width of said strip and aid in localizing saidwidening of said strip to the portion thereof inthe immediate vicinityof said metal member.

References Cited UNITED STATES PATENTS 1,909,704 5/1933 Morseth 2191072,107,831 2/1938 Morseth 219107 2,174,928 10/ 1939 Rumenschneider et a1.21981 2,344,790 3/1944 Schryber 219--81 2,376,762 4/ 1945 Ferguson219107 2,481,626 9/1949 Schryber 2l9-107 X 2,965,744 12/1960 Busse219107 3,047,712 7/1962 Morris 219-107 3,140,378 7/ 1964 Benninghoff219--107 X RICHARD M. WOOD, Primary Examiner.

B. A. STEIN, Assistant Examiner.

